Head and body length is 240-370 mm and tail length is 316-400 mm. Weight range from 0.6 to 1.0 kg. The soft, dense fur is silvery gray to dark gray above and gray, buff or brownish beneath. There are three dark brown or black lines radiating from the outer edges of the eyes and the bridge of the nose to the top of head and these are bordered by gray. The eyes are very large and closely set. The muzzle is unfurred and the ears are quite small. The densely furred tail is nonprehensile. There is a sac below the chin which can be inflated at will and gives resonance to the voice.

Aotus are found in forests from sea level to 2,100 meters. Owl monkeys are nocturnal and arboreal, sleeping in nests during the day in tree hollows and woody vines. The diet consist mainly of fruits, nuts, leaves, bark, insects, gums and small vertebrates.

Family groups are comprised of two to five individuals including an adult pair and their offspring from the last three breeding seasons. There is a single 80 gram baby born after a gestation period of 150-153 days. Sexual maturity is reached at 2 years of age for both males and females.

A. trivirgatus is found in Venezuela, south of Rio Orinoco, south to Brazil, north of Rios Negro and Amazon.